MR ductography

ABSTRACT

A magnetic resonance system and method are described for performing an improved magnetic resonance ductography which gives better resolution and higher signal to noise ratio than known systems and methods. Use is made of a small coil together with a post processing technique addressed to the improvement of the sensitivity of the coil. The magnetic resonance sequence used is a fat suppressed T2 weighted turbo spin echo sequence.

The invention relates to a magnetic resonance system arranged to acquirea magnetic resonance data from a volume using a magnetic resonanceimaging system and a fat suppressed T2 weighted turbo spin echo sequenceand further using a coil arrangement for receiving signal from thevolume.

Female patients presenting with nipple discharge or where a dilatationof the ducts was seen on ultra-sound are candidates for furtherdiagnostic examination. Techniques are known in the prior art forperforming diagnostic procedures which will aid in making an accuratediagnostic, and in the case of carcinoma, will aid in staging, orestimation of further spread, of the disease pathology.

A form of imaging frequently used to investigate the phenomenon ofnipple discharge is ductography. This is a special type of contrastenhanced mammography that visualizes the ducts and the intraductalpathology, that is to say, lesions in the breasts. It is a pre-operativestudy that facilitates the surgeon in performing accurate surgery withminimal tissue loss. Based on the ductogram the surgeon will determinewhether either removal of the lesion will suffice or whether removal ofthe entire ductal system or even total mastectomy should be performed.

In the conventional technique, which is variously named ductography,galactography or ductogalactography, the suspected duct is dilated andcannulated with a dedicated needle by an interventional radiologist.After this preparation, approximately 1 ml of contrast agent is injectedinto the duct under investigation. Images are made with standard X-raymammography equipment

This procedure is painful for the patient and can only be performed by aspecially trained radiologist. In about 20–30% of the cases theprocedure is not successful, either because the cannulation is not donecorrectly or because there is extravasation of the contrast agent intothe parenchyma. The latter condition is also painful.

Conventional ductography will be difficult to perform on women who haveundergone severe nipple surgery and on women with nipple retraction.Some patients suffer from allergic reactions to the contrast agentshortly after the procedure. Further, the whole procedure takes aboutone hour and requires the assistance of a trained nurse and amammography technologist in addition to the presence of the radiologist.In addition to the disadvantages already mentioned, the method exposesthe patient to ionizing radiation.

An alternative technique using magnetic resonance imaging has beendeveloped recently, for example in “MR Imaging in Patients with NippleDischarge: Initial Experience”, Greenstein Orel et al., Radiology 2000,216:248–254. In this method, a fat-suppressed T2 weighted turbo spinecho sequence is used to image the breast. This new technique ofmagnetic resonance ductography has produced immediate advantages overthe more traditional form of ductography. In particular, it is possibleto image the whole ductal structure in one scan. Conventionalductography is limited to the duct where the needle is inserted. It isalso now possible, using this new method, to visualize multiple lesionson one duct even if the a lesion is completely obstructing the duct andto determine the malignancy of a lesion based on shape characteristicsand the infiltration of the lesion into the duct. It is possible to showthe outside of the duct and not just the lumen as in the conventionalmammography technique. The new technique therefore has improvedspecificity. There are other advantages to using magnetic resonanceinstead of contrast enhanced mammography and these include the abilityto perform diagnostic imaging on every patient disregarding theirmedical history or possible allergic reactions to contrast agents, andthe reduction of overall patient exposure to ionizing radiation.

Unfortunately, the spatial resolution of the images acquired is not veryhigh. This reduces the visual separation in the image and means thatvery small objects are not reproduced in the image. The anatomical orderof magnitude of the ducts within the ductal systems of the mammary glandis very small, of the order of only 0.5 mm to 1 mm. The size of anylesions might also be only 0.5 mm to 1 mm and so a higher resolutionwould be advantageous. In addition, high spatial resolution imagesnormally have a low signal-to-noise ratio.

It is an object of the invention to produce a magnetic resonance systemfor acquiring a magnetic resonance ductography scan which has bothhigher resolution and a higher signal to noise ratio. This is achievedusing the invention in which the coil arrangement includes a small coilof diameter between 3.7 cm and 5.7 cm and also includes a body coil, thesmall coil of diameter between 3.7 cm and 5.7 cm is used for receivingthe magnetic resonance signal from the volume, the system further beingarranged to, correct the magnetic resonance data received from the smallcoil of diameter between 3.7 cm and 5.7 cm using auxiliary valuescalculated from a first auxiliary measurement acquired from the bodycoil and from a second auxiliary measurement acquired from the smallcoil of diameter between 3.7 cm and 5.7 cm.

The invention also relates to a method for acquiring a magneticresonance scan.

A microscopy coil, with a diameter of only 4.7 cm is used as a surfacecoil to acquire signal data from the ductal system. The construction ofthis coil allows the acquisition of signal locally with a very highsignal-to-noise ratio. This high signal to noise ratio is used toincrease the spatial resolution by acquiring a 512 matrix for a 7 cmfield of view, resulting in a 0.137 mm resolution. The coil is placedright above the ducts under examination. The method can also be usedwhere there is evidence of a pre-existing lesion, in which case the coilis placed directly over the lesion.

The size of the coil is chosen to cover the nipple area, or areola, ofthe breast. As such any diameter between 3.7 cm and 5.7 cm may be foundto be useful, with the range of 4.2 cm and 5.2 cm giving good results. Adiameter of 4.7 cm has been found to be particularly advantageous.

The high resolution is needed to get an image sharp enough to give aclinically useful differentiation of the shape of the lesion. This shapeis correlated to the malignancy of the lesion.

An inherent property of these small coils which have a very highsensitivity locally is that their signal yield further away from thecoil is low. This problem is overcome by using a post-processingtechnique which corrects for insensitivity. This correction technique isbased on the measurement of the sensitivity profile of the receivercoil. Since the sensitivity is actually measured the correction for itcan be perfect resulting in a flat signal level. The technique isperformed by acquiring auxiliary signals from both the small coil itselfand also from a body coil. These auxiliary signals are used to produceauxiliary values which are then used to correct the image data from thesmall coil. The technique is known to persons skilled in the art by thename of CLEAR.

The combination of the use of the microscopy coil to receive the signaland the CLEAR post-processing to correct for signal inhomogeneitiesresults in ductographic images with high diagnostic value.

The method for acquiring a magnetic resonance image using magneticresonance data from a volume uses a fat suppressed T2 weighted turbospin echo sequence in combination with a coil arrangement for receivingsignal from the volume. The coil arrangement includes a small coil ofdiameter between 3.7 cm and 5.7 cm and also includes a body coil. Inparticular, a coil of diameter 4.7 cm can be used. The small coil isused for receiving the magnetic resonance signal from the volume and sois placed directly onto the volume of interest. The magnetic resonancedata received from this coil is then corrected using auxiliary valuescalculated from a first auxiliary measurement acquired from the bodycoil and from a second auxiliary measurement acquired from the smallcoil itself.

These and further aspects of the invention will be explained using thefollowing figures.

FIG. 1 shows an example of a coil used in the invention.

FIG. 2 shows an example of ductal lesions which can be imaged using theinvention.

FIG. 3 shows a maximum intensity projection of the same case as shown inFIG. 2.

FIG. 1 shows an example of a coil used in the invention, shown againstan adult hand for comparison.

FIG. 2 shows an example of ductal lesions which can be imaged using theinvention. It shows multiple lesions in one duct indicated by arrows.The inplane resolution is about 0.140 mm.

FIG. 3 is a maximum intensity projection, or MIP, of the same caseshowing the complete ductal structure from the nipple down to the chest.The MIP clearly shows the advantage of using the post processingtechnique to correct for insensitivity of the small coil used.Homogeneous signal intensity over the whole ductal structure is shown.The width of the duct at the nipple is about 1.5 mm.

1. A magnetic resonance system arranged to acquire a magnetic resonancedata from a volume using a magnetic resonance imaging system and a fatsuppressed T2 weighted turbo spin echo sequence and further using a coilarrangement for receiving signal from the volume, wherein, the coilarrangement includes a small coil of diameter between 3.7 cm and 5.7 cmand also includes a body coil, the small coil of diameter between 3.7 cmand 5.7 cm is used for receiving the magnetic resonance signal from thevolume, the system further being arranged to correct the magneticresonance data received from the small coil of diameter between 3.7 cmand 5.7 cm using auxiliary values calculated from a first auxiliarymeasurement acquired from the body coil and from a second auxiliarymeasurement acquired from the small coil of diameter between 3.7 cm and5.7 cm.
 2. A magnetic resonance system as claimed in claim 1, whereinthe small coil has a diameter of between 4.2 cm and 5.2 cm.
 3. A methodfor acquiring magnetic resonance data from a volume using a magneticresonance imaging system and a fat suppressed T2 weighted turbo spinecho sequence and further using a coil arrangement for receiving signalfrom the volume, wherein, the coil arrangement includes a small coil ofdiameter between 3.7 cm and 5.7 cm and also includes a body coil, thesmall coil of diameter between 3.7 cm and 5.7 cm is used for receivingthe magnetic resonance signal from the volume, the method furthercomprising, correcting the magnetic resonance data received from thesmall coil of diameter between 3.7 cm and 5.7 cm using auxiliary valuescalculated from a first auxiliary measurement acquired from the bodycoil and from a second auxiliary measurement acquired from the smallcoil of diameter between 3.7 cm and 5.7 cm.